Sample reference intervals for hematological assays in healthy pregnancy.Īctivated partial thromboplastin time (APTT) (s) 3 Red cell mass also returns to normal levels by 6 weeks postpartum. 1 Red blood cell mass does not increase until approximately 20 weeks' gestation, and increases approximately 30% above the non-pregnant state. Plasma volume starts to fall from the 6th postpartum day, reaching non-pregnant levels at 6 weeks postpartum. Plasma volume starts to increase from the 6th gestational week, being approximately 10% above pre-pregnancy levels in early second trimester, then rising rapidly reaching levels greater than 50% above pre-pregnancy levels by 26 weeks' gestation, then plateauing for the remainder of pregnancy. Healthy pregnancy is associated with a fall in hemoglobin (Hb) and hematocrit due to the increase in plasma volume being greater than the increase in red cell mass, and occurring at an earlier gestation (Table 1). Wherever possible clinicians should use a reference interval specific to the laboratory that has performed the test. There is significant variability between laboratories depending on the method of testing, the assay used and population factors. Physiological changes in pregnancy may result in significant changes in normal values for many hematology assays, and as such results may be misinterpreted as abnormal or mask a pathological state. Interpretation of laboratory investigations relies on reference intervals. See end of chapter for details INTRODUCTION By completing 4 multiple-choice questions (randomly selected) after studying this chapter readers can qualify for Continuing Professional Development awards from FIGO plus a Study Completion Certificate from GLOWM
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